Oils resistant to highly reactive chemicals

ABSTRACT

Perfluoropolyether lubricating oils resistant to degradation by a variety of corrosive chemicals, including boron trifluoride, sulfur tetrafluoride and uranium hexafluoride, are characterized by being substantially free from components reactive to uranium hexafluoride.

Erdann et al.

[451 .lanZZ, 11974 4] oiLs RESHSTANT T0 HIGHLY REACTIVE CHEMICALS [75] Inventors: Dietrich Erdmann; lstvan Namnyi;

Briino llarnpel, all of Darmstadt; Werner Herbert, Markdorf, all of Germany [73] Assignee: Merck Patent Gesellsclmit mit besclirankter Haitnng, Darmstadt, Germany 22 Filed: Feb. 17, 1971 211 Appl.No.:116,230

[30] Foreign Application Priority Data Feb. 18, 1970 Germany P 20 07 245.1

[52] US. Cl. 252/54, 260/615 BF [51] lm. CL... C10m 1/30 [58] Field of Search 252/54; 260/615 BF [56] References Cited UNITED STATES PATENTS 3,125,599 3/1964 Wamell 260/615 BF X 3,214,478 10/1965 Milian 260/615 BF 2,895,806 7/1959 Sheldon et a1. 23/230 R Primary Examiner-Daniel E. Wyman Assistant Examiner-W. Cannon Attorney, Agent, or FirmMillen, Raptes & White [57] ABSACT 12 Claims, No Drawings OILS RESISTANT T HIGHLY lltlEAC'llllVE CHEMICALS It is known that perfluoropolyether based lubricating oils exhibit a high resistance to the stresses which ordinarily occur in the technical field, especially against the effect of many chemicals. However, it was found that even these oils show signs of decomposition which have an adverse effect on their lubricating capacity when they come into contact with very reactive chemicals, such as, for example, boron trifluoride, sulfur tetrafluoride, or uranium hexafluoride.

SUMMARY OF THE INVENTION According to this invention, lubricating oils resistant to very reactive chemicals are obtained by treating perfluoropolyether oils with uranium hexafluoride and separating, in a conventional manner, the components precipitated during this treatment and/or converted into volatile products. The resulting lubricating oils are especially suitable for the lubrication of points of friction in fast-running machine parts exposed to the effect of uranium hexafluoride.

Accordingly, in one aspect, this invention relates to perfluoropolyether lubricating oils resistant against highly reactive chemicals which are substantially free from uranium hexafluoride reactive components.

In another aspect, this invention relates to a process for the preparation of perfluoropolyether lubricating oils resistant against very reactive chemicals by treating a perfluoropolyether with uranium hexafluoride and separating therefrom the thus-precipitated components and/or the thus-produced volatile products, as well as any excess uranium hexafluoride present therein.

In a further aspect, this invention relates to lubrication of friction points which are exposed to uranium hexafluoride with a lubricating oil of this invention.

DETAILED DISCUSSION The perfluoropolyether lubricating oils of this invention generally have molecular weights of between about 1,000 and 4,000, preferably between 1,800 and 2,600; a density ordinarily ranging between about 1.7 and 2.1 g./cm a viscosity of about 20-300, preferably 30-100 centistokes at 20 C.; and a vapor pressure of between about and 10" mm. Hg at C. These oils do not exhibit any undesired change in properties when used in the presence of uranium hexafluoride in the bearings of high-speed machines, even after longer operating periods at very high rates of revolutions. They are characterized by being substantially free from uranium hexafluoride reactive components.

The starting materials for the preparation of the lubricating oils of this invention are commerically available perfluoropolyether oils. Especially suitable startin g products for the novel lubricating oils of the present invention are perfluoroalkylene oxides whose alkylene groups contain 14 carbon atoms, i.e., polyoxyperfluoromethylenes, perfluoropolyethylene oxides, perfluoropolypropylene oxides, and perfluoropolybutylene oxides. Preferred starting materials are perfluoropolyethylene oxide and perfluoropolypropylene oxide lubricating oils having molecular weights between about 1,000 and 4,000, which boil between about 70 and 300 C. at pressures of between about 0.1 and 0.5 mm. Hg and exhibit a kinematic viscosity of between about 20 and 300 cs at 20 C. Perfluoropolyether oils of this type are commercially available under the trademark Fomblin (Montecatini Edison S.p.A., Italy). Mixtures of the above-described perfluoropolyethers can also be employed as the starting materials for the preparation of the lubricating oils of this invention.

The lubricating oils of this invention are prepared by treating a perfluoropolyether oil as described above with uranium hexafluoride, e.g., at a temperature between 0 an C. For the treatment of one part by weight of perfluoropolyether oil, preferably about 0.01 10 parts by weight of uranium hexafluoride are employed. The thus-formed solid and/or volatile products are separated in a conventional manner, along with any excess uranium hexafluoride, optionally after first cooling the treated oil.

Surprisingly, the thus-treated lubricating oils are also resistant against attack by a variety of very reactive fluorine compounds. The exact nature of the conversion which the perfluoropolyether oil has undergone as a result of the treatment of this invention has not yet been unequivocally determined. However, an essential part in the improvement probably is the result of the removal of the component thereof which can be precipitated by the treatment with uranium hexafluoride.

If the treated lubricating oil must meet specific, narrowly defined requirements, for example with respect to the vapor pressure, viscosity, etc., the treated oil can thereafter be fractionated in a conventional manner, for example by distillation.

A general mode of conducting the process of this invention is to pass uranium hexafluoride through a vessel filled with a perfluoropolyether. In a special embodiment, this is effected by allowing gasified uranium hexafluoride to flow under its own pressure into the oil through an aperture disposed beneath the surface of the perfluoropolyether oil. Suitably, the gas inlet port is arranged at a point of the reaction vessel which is as low as possible. In order to distribute the gas more evenly, the inlet port can be fabricated in the form of a screen plate or a porous plate. Additionally, the lubricating oil can be agitated during the gas introduction.

In another special embodiment of this process, the gaseous uranium hexafluoride is drawn under vacuum through the perfluoropolyether oil. The vacuum used depends partially on the temperature of the uranium hexafluoride and also on the height of the oil layer above the gas inlet port. In correspondence with these variables, the vacuum can be varied between 1 and 700 mm. Hg. For example, if the process is conducted at room temperature with an oil level above the gas inlet of about 30 cm., a pressure of 25 mm. Hg can be employed. By additionally agitating the oil, the contact between the perfluoropolyether oil and the uranium hexafluoride is intensified in this mode of operation also.

In another embodiment of the process of this invention the perfluoropolyether oils are treated with uranium hexafluoride in a countercurrent process. For this purpose, the perfluoropolyether oil is allowed to flow, for example, down and through a packed column and the uranium hexafluoride is conducted upwardly from below countercurrently to the oil. By varying the type and size of the packing, the flow rate and the surface area of the oil coming into contact with the uranium hexafluoride can be regulated. In a specific embodiment of this process, a thin-film reactor is employed wherein the downwardly flowing oil is distributed, by a rotating wiper, onto the surface of the reaction vessel in a uniformly thin film. Also, in these methods which operate ina countercurrent manner, the uranium hexafluoride can either be introduced under pressure into the reaction vessel, or it can be drawn through under reduced pressure. In countercurrent apparatus one or both reactants can advantageously be conducted therethrough in a cyclic manner, thereby effecting an economical utilization of the uranium hexafluoride.

In the embodiments of the process of this invention wherein the perfluoropolyether oil is treated with gaseous uranium hexafluoride, the duration of the treatment is dependent on the amount and the quality of the perfluoropolyether oil employed and ranges, e.g., when using 1,000 g. of perfluoropolyether oil of commercial quality, between minutes and 8 hours. The throughput of uranium hexafluoride is preferably 30-300 g. per hour per kilogram, more preferably 50-150 g. per hour per kilogram of oil.

It proved to be advantageous, during the treatment of the perfluoropolyether oils with uranium hexafluoride, to exclude air and especially moisture, which liberates hydrogen fluoride by hydrolysis of the uranium hexafluoride, which hydrogen fluoride has a strongly corrosive effect on the equipment employed.

In the treatment of the perfluoropolyether oil with gaseous uranium hexafluoride, the latter can be introduced in a diluted form, e.g., in a mixture with a dry inert gas, e.g., nitrogen, argon, or helium. In such gaeous mixtures, the proportion of uranium hexafluoride is usually l-95 percent, preferably 5-60 percent.

The treatment of the perfluoropolyether. oils is suitably conducted at temperatures between about 0 and 100 C. The process of the present invention can also take place at lower or higher temperatures. However, at temperatures below 0 C., the rate of reaction is ordinarily too low for an economical conductance of the process and at temperatures of about 100 C., undesired decomposition of the perfluoropolyethers due to the uranium hexafluoride occasionally occurs. Preferably, the process of this invention is carried out between about room temperature and about 85 C.

When the treatment of perfluoropolyether oil according to this invention is effected at an elevated temperature, the heating can be conducted in various ways. When passing the uranium hexafluoride through the oil, it is often especially advantageous to heat the reaction vessel and to transfer the heat to the oil by thorough agitation. Of course, it is also possible to introduce preheated uranium hexafluoride through the oil. When conducting the process in a countercurrent manner, the column can be heated, e.g., with a heating mantle. However, it is likewise possible to introduce oil previously heated to the desired reaction temperature or pass preheated uranium hexafluoride countercurrently therethrough. Heating one or both reactants prior to introducing them into the reaction chamber is advantageous when one or both of the reactants are introduced in a cyclic manner.

In another embodiment of the process of this invention, the perfluoropolyether oil is reacted with uranium hexafluoride in a sealed reaction vessel. This can be done in a simple manner by introducing, into a reaction vessel filled with perfluoropolyether oil, finely divided, solid uranium hexafluoride, sealing the vessel, and agitating or shaking until the desired degree of conversion has been attained. Suitably, pressure reaction vessels are employed in this process so that it is possible to operate at an elevated temperature, e.g., above the point of sublimation of the uranium hexafluoride (56 C.). Especially advantageous is a shaker autoclave made of a corrosion-proof material. The weight ratio of perfluoro-polyether oil to uranium hexafluoride can be varied within wide limits. This ratio depends primarily on the quality of the perfluoropolyether oil employed and ranges ordinarily between about l and 1 1, preferably about 50 l and 2 1. The duration of the treatment can range from a few minutes, e.g., 15 minutes to several hours, e.g., 24 hours or longer. Preferred reaction times are between about 1 and 5 hours. If the process is conducted at an elevated temperature, shorter treatment periods are usually sufficient.

In the treatment of the perfluoropolyether oils with uranium hexafluoride, a light-colored, fine-crystalline or amorphous product is usually precipitated. When conducting the treatment at an elevated temperature, such a material occasionally separates only after cooling. The separating step is conducted in a conventional manner, for example by filtration, preferably either pressure or vacuum-filtering. The use of filters of an inorganic material, e.g., glass fiber filters or filter layers of other inert materials, e.g., silicon dioxide or aluminum oxides, proved to be advantageous. Of course, the filter material must be well cleaned and absolutely dry. Furthermore, the separation can also be effected by distillation, wherein simultaneously separation of the distillate into different fractions can be conducted. The properties of such fractions vary within narrow limits. Such a distillation is ordinarily effected under reduced pressure, preferably under a pressure of below 1 mm. Hg.

The removal of any excess uranium hexafluoride present in the product is conducted according to standard methods, for example by conducting an inert gas, such as nitrogen or argon, therethrough, and/or by heating and/or degasification under reduced pressure. When the excess uranium hexafluoride is driven off by passing an inert gas therethrough, if desired, the final product can subsequently be degasified by heating and- /or under reduced pressure.

In case volatile products are produced in the process of this invention instead of or together with the solid products, these are discharged when the process is conducted with gaseous uranium hexafluoride, usually at least partially together with the unreacted uranium hexafluoride which exits from the reaction vessel. Volatile reaction products can also be removed when the excess uranium hexafluoride is driven off, as well as during the final degasification and/or distillation of the final product.

The above-described process can be repeated to ensure complete removal of all uranium hexafluoride reactive components in the oil.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever.

EXAMPLE 1 Uranium hexafluoride is drawn under vacuum, with the exclusion of air and moisture, for 2 hours at room temperature and 25 mm. Hg, through a column having a length of 30 cm. (diameter 5.0 cm.) with an inlet port for gases at the bottom, containing 200 g. of perfluoropolyether oil consisting essentially of pert'luoropolyethylene oxides and perfluoropolypropylene oxides having a molecular weight range of between l,000'and 4,000, boiling at 190-290 C. under 0.3 0.4 mm. Hg, and exhibiting a viscosity at 20 C. of about 250 cs (Fomblin Y 25, producer: Montecatini Edison S.p.A., Italy). Thereafter, the oil is filtered through a press filter, and the treatment with uranium hexafluoride is repeated. After another filtering-off step, dry nitrogen is passed through the oil for one hour, and the oil is then degasified for 1 hour at 100 C. and 0.3 mm. Hg.

EXAMPLE 2 In the apparatus described in Example 1, gaseous uranium hexafluoride is drawn under vacuum at 85 C. and 25 mm. Hg, with the exclusion of air and moisture, through 100 g. of perfluoropolyether oil consisting essentially of perfluoropolyethylene oxides and perfluoropolypropylene oxides having molecular weights of between 1,000 and 4,000, boiling at 0.3 0.4 mm. Hg at 802l0 C., and exhibiting, at 20 C., a viscosity of about 35 cs (Fomblin Y 04, producer: Montecatini Edison S.p.A., ltaly). Thereafter, the uranium hexafluoride is driven off by passing dry nitrogen therethrough, and the oil is filtered, after cooling, through a press filter. This succession of treatment steps is repeated, and the oil is then degasified at 100 C. and 0.3 mm. Hg.

EXAMPLE 3 Of 481 g. of perfluoropolyether oil consisting essentially of perfluoropolyethylene oxides and perfluoropolypropylene oxides having molecular weights of between 1,000 and 4,000, boiling at 0.3 0.4 mm. Hg at 802l0 C., and exhibiting a viscosity, at 20 C., of about 35 cs (Fomblin Y 04), the portion which distills at 80 to 140 C. at 0.5 mm. Hg, is distilled off through a Vigreux column. Through the remainder (316 g. of a colorless, clear oil), uranium hexafluoride is drawn under vacuum at room temperature for 2 hours at 25 mm. Hg, at a rate of about 130 g. per hour. During this procedure, white flakes separate which are removed by filtration. The treatment with uranium hexafluoride is repeated twice until no further flake formation is observed. Thereafter, the excess uranium hexafluoride is driven off by passing dry argon through the raction product for l k hours. The oil is then degasified for 2 hours at 80 C. and 0.1 mm. Hg. A lubricating oil which is completely resistant to highly reactive chemicals is obtained having a molecular weight of 2,150 2,250, a density of 1.90 g./rnl. and a refractive index n,, of 1.2960. The vapor pressure at 20 C. is 8 X 10 mm. Hg, and the viscosity at C. is 57.8 cs.

EXAMPLE 4 Wtih the exclusion of air and moisture, uranium hexafluoride is passed at a rate of 100 g. per hour for 2 hours at 85 C. through 200 g. of a perfluoropolyether oil prepared by distillation as set forth in Example '3. After cooling, the white flakes which separated from the oil are vacuum-filtered. The treatment is repeated twice at 85 C. After no further flakes are precipitated during the second repetition, the uranium hexafluoride is driven off by introducing dry ni trogen for 1 hour, and the oil is then degasified at C. and 0.5 mm. Hg. The thus-obtained oil exhibits the same properties as the product prepared according to Example 3.

3 5 ml. of this oil is filled into a bearing of a highspeed machine where the oil is exposed to the effect of uranium hexafluoride. After an operating period of 24 hours at 40,000 r.p.m., no undesired changes can be seen in the oil.

EXAMPLE 5 A shaker autoclave having a capacity of 500 ml. is charged, in an absolutely dry atmosphere at a temperature of 5 C., with 500 g. of perfluoropolyether oil consisting essentially of perfluoropolyethylene oxides and perfluoropolypropylene oxides having molecular weights of between 1,000 and 4,000, boiling at 0.3 0.4 mm. Hg at 190 290 C., and exhibiting a viscosity, at 20 C., of about 250 cs (Fornblin Y 25), and with 220 g. of uranium hexafluoride. After closing the autoclave, the air present above the charge is displaced by dry nitrogen, and the autoclave is sealed. Over a period of l /2 hours, the charge is gradually heated to 70 C. under constant shaking deflections per minute), and the shaking is continued at this temperature for 2 hours. The pressure rises to about 3 atmospheres during this step. Thereafter, the reaction mixture is allowed to cool under continued shaking, the pressure dropping again almost to normal pressure during this procedure. Then, the vessel is opened while passing dry nitrogen thereover and the contents are filtered through a press filter. The filtrate is distilled under a nitrogen atmosphere at 0.1 mm. Hg. The fraction going over at between and 250 C. is separately collected. The product exhibits a density of 1.88 g./ml. and a viscosity of cs at 20 C.

EXAMPLE 6 A perfluoropolyether oil consisting essentially of perfluoropolyethylene oxides and perfluoropolypropylene oxides having molecular weights of between 1,000 and 4,000, boiling at 0.3 0.4 mm. Hg at 80 210 C., and exhibiting a viscosity of about 35 cs at 20 C. (Fomblin Y 04), is allowed to pass at a rate of 150 ml. per hour from a dropping funnel through a column having a length of 150 cm. and a diameter of 3 cm. and filled with Raschig rings (2 mm. diameter), through which column uranium hexafluoride is continuously drawn under vacuum from the bottom toward the top at a rate of 200 g. per hour. During this procedure, the column is heated externally to 50-S 5 C. The oil dripping from the bottom of the column is passed through a 611 porous sintered glass plate, is collected with the exclusion of air and moisture and once more passed through the column. Thereafter, the oil is cooled, again filtered, and degasified at 80 C. and 0.1 mm. Hg for 1 hour.

In a test conducted under actual use conditions as described infix nuzlsfitzth aqi .ezthL t l Same advantageous properties as the oil prepared in accordance with Example 4.

Th eprecedingexamples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

What is claimed is:

l. A process for the preparation of a perfluoroalkylene oxide lubricating oil resistant to highly reactive chemicals which comprises treating one part by weight of a perfluoropolyalkylene oxide lubricating oil of a molecular weight of between about 1,000 and 4,000 whose alkylene groups each are of 1-4 carbon atoms, with about 0.01 10 parts by weight of uranium hexafluoride at a temperature between and 100 C. and separating therefrom the thus-produced solid and volatile components and any residual uranium hexafluoride.

2. A process according to claim 1 wherein the perfluoropolyalkylene oxide is selected from the group consisting of perfluoropolyethylene oxides, perfluoropolypropylene oxides, and mixtures thereof.

3. A process according to claim 1 wherein the starting perfluoroalkylene oxide has a molecular weight between about 1,800 and 2,600.

4. A process according to claim 1 wherein the perfluoropolyethers are treated with gaseous uranium hexafluoride.

5. A process according to claim 1 wherein the perfluoropolyethers are treated under pressure with uranium hexafluoride in a sealed reaction vessel.

6. Lubricating oils resistant to highly reactive chemicals consisting essentially of perfluoroalkylene oxides of a molecular weight of between about 1,000 and 4,000 whose alkylene groups each are of l-4 carbon atoms, substantially free from uranium hexafluoride reactive components, produced according to the process of claim 9.

7. A lubricating oil according to claim 6 wherein the perfluoropolyalkylene oxide is selected from the group consisting of perfluoropolyethylene oxides, perfluoropolypropylene oxides, and mixtures thereof.

8. A lubricating oil according to claim 6 having a molecular weight range between about 1,800 and 2,600.

9. A lubricating oil according to claim6 having a viscosity of about 20-300 centistokes at 20 C.

10. A lubricating oil according to claim 6 having a vapor pressure of 10 to 10 mm. Hg at 20 C.

11. A lubricating oil according to claim 6 having a viscosity of about 20-300 centistokes at 20 C. and a vapor pressure of 10 to 10 mm. Hg at 20 C.

12. A lubricating oil according to claim 6 selected from the group consisting of perfluoropolyethylene oxides, perfluoropolypropylene oxides and mixtures thereof, having a viscosity of about 20-300 centistokes at 20 C. and a vapor pressure of 10- to 10' mm. Hg at 20 Cf 

2. A process according to claim 1 wherein the perfluoropolyalkylene oxide is selected from the group consisting of perfluoropolyethylene oxides, perfluoropolypropylene oxides, and mixtures thereof.
 3. A process according to claim 1 wherein the starting perfluoroalkylene oxide has a molecular weight between about 1, 800 and 2,600.
 4. A process according to claim 1 wherein the perfluoropolyethers are treated with gaseous uranium hexafluoride.
 5. A process according to claim 1 wherein the perfluoropolyethers are treated under pressure with uranium hexafluoride in a sealed reaction vessel.
 6. Lubricating oils resistant to highly reactive chemicals consisting essentially of perfluoroalkylene oxides of a molecular weight of between about 1,000 and 4,000 whose alkylene groups each are of 1-4 carbon atoms, substantially free from uranium hexafluoride reactive components, produced according to the process of claim
 9. 7. A lubricating oil according to claim 6 wherein the perfluoropolyalkylene oxide is selected from the group consisting of perfluoropolyethylene oxides, perfluoropolypropylene oxides, and mixtures thereof.
 8. A lubricating oil according to claim 6 having a molecular weight range between about 1,800 and 2,600.
 9. A lubricating oil according to claim 6 having a viscosity of about 20-300 centistokes at 20* C.
 10. A lubricating oil according to claim 6 having a vapor pressure of 10 4 to 10 7 mm. Hg at 20* C.
 11. A lubricating oil according to claim 6 having a viscosity of about 20-300 centistokes at 20* C. and a vapor pressure of 10 4 to 10 7 mm. Hg at 20* C.
 12. A lubricating oil according to claim 6 selected from the group consisting of perfluoropolyethylene oxides, perfluoropolypropylene oxides and mixtures thereof, having a viscosity of about 20-300 centistokes at 20* C. and a vapor pressure of 10 4 to 10 7 mm. Hg at 20* C. 